Moderator: VelvetGeorge
Yep, I must have missed it because I looked at my hand drawn schematic and it was there. I've updated both the PDF and the image file. Thanks for the feedback!Bug2222 wrote:...I can't find C11 (10nF) in your schematic. It should be connected with R7 (B+5)?
) you'll get rid of it. I did that because I didn't use the reverb at all and the hiss is way lower now. With the amp at full blast on the Normal channel the hiss is almost inaudible and the Top Boost channel has a manageable amount of it. The downside of it is that you will lose the reverb. 
By raising C34 to 47n you shift the bass response higher effectively attenuating some really low bass frequencies. Once again it's the value used in the Dallas circuit.I see you have also chanced the C34 cap in your amp. What effect has this change?
If you look closely R5 and R6 are 220k (red-red-black-orange-brown). C5 is the stock values (22n) because I wanted a bit less bass.it seems that you did not have changed R5, R6 and C5 in the normal channel mod.
R1 forms a voltage divider with VR1 and limits the output of that stage to 60% max. Jumping it allows you to get the full signal into the PI. This was also implemented by Vox to prevent the op-amp from clipping. C4 is a treble bleed cap that bypasses VR1 for high frequencies making the channel shrill at low gain values.I think that bring's more gain in normal channel without the 330k resistor. Removing of the C4 cap eliminates the icepick high’s (why not also in the top boost channel R8/C67?).
Is the other way around, the gain increases as you raise the plate resistance. As I said earlier C5 is a coupling cap, higher values will allow lower frequencies to pass.The 220K resisters are reducing the gain in V1/V2 (instead of 100K)? Is that right? What does the changing of the value of C5?
Not at all, I didn't have metalfilm resistors of that value around so I went with those.In your bypassing mod you're using carbon resistors. Is there any special reason for that?
You'll definitely have to remove the main board to perform the mod. But it's easier than you think. It's held by the pot's lock-nuts and 3 screws. Remove all that and gently move the board back from the front plate until you get enough clearance from the pots to rotate it to a vertical position. No need to unplug anything from it.[/quote]... must I remove the complete mainbord for that?
It was part of the op-amp circuit. I wanted to get the circuit as close to the original as possible so I could hear how it sounded and then tweak it to my taste.Why is C19 in the signal path to the treble pot no longer needed?
